1. Field of the Invention
This invention relates to internal combustion engine valvetrain components and, more particularly, to valve rotators.
2. Discussion of the Related Art
Valve rotators are commonly used in some internal combustion engines to provide positive valve rotation during each cycle of an opening phase of engine valve actuation. It is known and appreciated that even slight rotation of a valve during use can increase engine service intervals and extend valvetrain use life by, e.g., minimizing burning and guttering type wear of valves, reducing thermal differentials across each individual valve, reducing carbon buildup on the valves, promoting valve stem lubrication, and/or other benefits.
Known valve rotators are typically classified as being either garter type valve rotators or bearing ball rotators which are commonly referred to as ball type valve rotators. Both garter and ball type valve rotators can be installed in place of a valve spring retainer on the top of a valve spring, or as an additional valvetrain component installed under a valve spring. In either case, whether used as a supplemental valvetrain component, or a replacement component, the valve rotators function by, e.g., utilizing energy associated with valve spring compressive forces and converting such energy into rotational movement of a rotator body within a rotator housing and correspondingly rotating the valve itself.
Garter type valve rotators can be configured as relatively lightweight and relatively inexpensive components. Garter type valve rotators include a garter spring defined by a helically wound spring member that is bent into an annular arrangement, giving it a circular perimeter shape. In this configuration, as the valve spring is compressed and loaded, a spring disk within the garter type valve rotator deflects. The spring disk deflection is transmitted through the garter spring, folding its coils down and forward, correspondingly shifting or rotating the rotator body and thus also the valve attached to it. When the valve spring unloads, the garter spring also unloads, restoring it to its default configuration. This cycle of garter spring loading and unloading, and pushing the valve into rotation, is repeated during subsequent valve actuation(s). In other words, this completes a cycle of valve rotation that is repeated with every opening and closing of the valve.
However, due to size constraints, garter springs of garter type valve rotators are made from relatively small diameter spring material. Correspondingly, the garter springs can have a relatively short use life due to, e.g., exposure to various fatigue forces, loading and unloading at a high rate of recurrence or frequency, temperature cycling between periods of use and non-use, and/or other factors or stresses endured during use.
In light of the above mentioned durability and reliability concerns associated with the garter springs of garter rotators, ball rotators are often preferred for certain implementations, such as for use in relatively larger engines. Ball rotators typically include a circularly shaped housing with multiple sloped pockets formed thereinto. Bearing balls, along with helical compression springs that bias them, are provided in the sloped pockets of the housing in a manner that biases the bearing balls toward shallow ends of the sloped pockets. The bearing balls and springs are further confined by a spring disk resting on a stepped flange of the rotator body, such that the spring disk and pockets, in combination, totally encapsulate the bearing balls and springs. During use, as the valve spring is compressed and loaded, the spring disk deflects, transferring force from the valve spring into bearing balls of the rotator. Since the balls rest on the top of sloped surfaces of the pockets embedded in the flange of the rotator body, rolling motion of the bearing balls occurs which rotates the rotator body and thus also the valve attached to it.
For example, U.S. Pat. No. 2,397,502 discloses a known ball type valve rotator. The ball type rotator is placed on the top of the valve spring, replacing the valve spring holder, and includes a rotator body and housing, multiple bearing balls and cooperating helical springs, a spring disk. The rotator body has a tapered central section, an annular outer flange segment, and a stepped flange as a medial segment transitioning therebetween. The tapered central section connects to the valve, the stepped medial segment serves as a resting place for the spring disk, and the outer flange segment has multiple pockets formed thereinto. The pockets confine bearing balls and helical springs therein, and the bottom walls of the pockets are sloped. The bearing balls and springs are arranged so that the bearing balls bias toward shallow ends of the pockets. A circularly shaped housing encapsulates the bearing balls, springs, and spring disk, and it has a flange that serves as a seat for the valve spring. In this configuration, an inner edge of the spring disk rests on the stepped medial segment of the rotator body, whereas an outside edge of the spring disk rests on a bottom surface of the housing flange, whereby the spring disk carries the load of the compressed valve spring. Accordingly, the spring disk deflects proportionally to the magnitude of the valve spring force.
In other words, during engine operation, as the valve opens, the valve spring is being increasingly compressed, increasing the force applied to the spring disk which further deflects the spring disk and correspondingly decreases an effective height of the pockets containing the bearing balls. At this point, the spring disk rests mostly on the bearing balls, whereby the inner portion of the spring disk lifts away from and is no longer supported by the stepped medial segment of the rotator body. This transmits forces of the valve spring into the bearing balls that are confined in the pockets. Since the rotator body is no longer held by frictional forces defined between the stepped medial segment of the rotator body and the spring disk, the bearing balls are free to roll down into the deeper ends of the pockets, forcing the rotator body to shift circularly.
Namely, since the rotator housing and the spring disk stay attached to the valve spring, the rolling motion of the bearing balls is translated into a rotation of the rotator body and the valve attached to it. As the valve closes, the valve spring decompresses which lessens the force on the spring disk, making it return to its previous shape. Such relaxation of the spring disk increases the effective height of the pockets. As the effective height of each pocket increases, the bearing balls are pushed by the helical springs, back into the shallow ends of the pockets. This completes a cycle of valve rotation that is repeated with every opening and closing of the valve.
As with typical ball type valve rotators, those disclosed in U.S. Pat. No. 2,397,502 include a cast, machined, and hardened steel rotator body. This component is labor or process intensive to make, and is correspondingly relatively expensive. Furthermore, installing the multiple bearing balls, multiple springs, spring disk, and housing requires crimping a top rim of the housing over a top edge of the rotator body, and/or retaining the rotator housing and body with a wire retainer inserted in a grove within the rotator body. This is a labor or process intensive operation that yet further increases the end price of the total assemblage.
U.S. Pat. No. 6,588,391 discloses another known ball type rotator that functions similar to that seen in U.S. Pat. No. 2,397,502, but includes a rotator body that is made by joining two components instead of a single cast and machined component. A first component that is used to make the rotator body is stamped from sheet metal, has a deep drawn conical inner segment, and pockets are drawn from material at an outer flange portion. While forming such first components, during the drawing or pressing procedure, one end of the pocket is formed by shearing which leaves a gap or opening at the respective end. The second component that is used to make the rotator body is a holding ring that is used to retain and guide the bearing balls and their actuating springs, since the pockets formed into the first component are not sufficiently deep to house them. The first and second components are hardened and joined to each other by hump or bulge welding, forming a single unitary rotator body.
These components can be difficult to manufacture and assemble. Deep drawing the conical inner segment can be difficult to accomplish while maintaining suitably consistent material thickness required for structural integrity. It is noted that like other valvetrain components, valve rotators must meet stringent dimensional and structural requirements since they are subjected to high local stresses and fatigue forces of repeatedly valve opening and closing cycles. In addition, although the openings at the pocket ends can intake lubrication, they can also intake non-desired debris or other materials or substances. The corners or ends of the shear line, from which the pocket end openings are defined, can further tear, potentially compromising the structural integrity of the rotator body. It is further noted that the hardening and hump or bulge welding can be labor or procedurally intensive, increasing the end price of the valve rotator.
In typical prior art ball type valve rotators, the pockets that hold the bearing balls and springs have bottom walls that are rigid or inflexible, regardless of whether the pockets are formed by machining a casting, formed by drawing sheet material in a punch-pressing or other operation, or other configurations. It is further noted that in the dynamically changing high stress and load environment in which valve rotators operate, the forces that are applied to the valve rotators are rarely evenly distributed about the rotator body and/or housing. In other words, during use, valve rotator bodies and/or housings are subjected to highly localized applications of the input forces. The bearing ball(s) nearest such localized application of force therefore bears relatively more stress of the input force and carry more or even a majority of the load, as compared to the other bearing balls. This can create point loading between such bearing balls and the spring disk with sufficiently great force to create pitting in, or wear grooves into, the spring disk which can shortening its use life.